Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
  • H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
  • H03F3/087—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light with IC amplifier blocks
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/45—Differential amplifiers
  • H03F3/45071—Differential amplifiers with semiconductor devices only
  • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
  • H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
  • H03F2203/45—Indexing scheme relating to differential amplifiers
  • H03F2203/45136—One differential amplifier in IC-block form being shown
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
  • H03F2203/45—Indexing scheme relating to differential amplifiers
  • H03F2203/45528—Indexing scheme relating to differential amplifiers the FBC comprising one or more passive resistors and being coupled between the LC and the IC
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
  • H03F2203/45—Indexing scheme relating to differential amplifiers
  • H03F2203/45534—Indexing scheme relating to differential amplifiers the FBC comprising multiple switches and being coupled between the LC and the IC
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
  • H03F2203/45—Indexing scheme relating to differential amplifiers
  • H03F2203/45616—Indexing scheme relating to differential amplifiers the IC comprising more than one switch, which are not cross coupled

Definitions

• Photodiode-transimpedance amplifier combinations are used in a laser power control circuit for DVD applications.
• the first order limitation to achieving high speed in combination with high precision in this circuit lies with the magnitude of the photodiode parasitic capacitance.
• traditional circuits use the feedback resistor and diode capacitance time constant to set the dominant pole of the circuit. This time constant, divided by (1 + A VOL ) , where A VOL is the open loop gain of the amplifier, sets the bandwidth of the circuit. Note that the internal pole of the amplifier becomes the secondary pole.
• this circuit has several limitations.
• the open loop gain is limited by the need to have the secondary pole, contributed by the amplifier, out far enough in frequency so as to not contribute excessive phase shift in the closed-loop response, which leads to instability.
• limited open-loop gain limits the maximum value of the transimpedance-setting resistor, RF, in the feedback if we are to achieve a given bandwidth.
• CMFA current-mode-feedback amplifier
• CFMA' s have inherently low open loop input impedance (looking into the emitters of a complementary NPN, PNP pair).
• the secondary pole formed by the diode capacitance and the input resistance of the amplifier is an order of magnitude away from the required amplifier bandwidth and has no effect on circuit response.
• the amplifier can be compensated internally by conventional means and the magnitude of the open loop gain A VOL , is not limited.
• the CFMA approach has significant accuracy limitations. CFMA' s have extremely high input offset voltages and bias currents compared to voltage feedback amplifiers and this largely prevents their use in this application.
• Figure 1 shows a diagram of a prior art photodiode transimpedance amplifier.
• Figure 2 shows a diagram of a photodiode transimpedance amplifier circuit of one embodiment of the present invention.
• one embodiment of the present invention is a circuit 200 comprising an operational amplifier 202; an input acquisition loop 204; and an output acquisition loop 206.
• the output of the operational amplifier 202 can pass through the input acquisition loop 204 in a first phase and through the output acquisition loop 206 in a second phase.
• the circuit 200 can compensate for the input offset voltage and bias current errors of the operational amplifier.
• the operational amplifier 202 can be a CMFA amplifier, such as a transimpedance amplifier.
• operational amplifier 202 can be an operational transimpedance amplifier (OTA).
• OTA operational transimpedance amplifier
• a voltage drop across a resistor, Rp 2 , in the output acquisition loop 206 can compensate for the input offset voltage of the operational amplifier.
• Another resistor, Rvos can switched in across the inputs to the operational amplifier in the second phase.
• the value of resister Rvos can be equal to the value of resister RF2-
• a photodiode 208 can produce an input current to the circuit.
• the photodiode can be used to detect information from an optical medium, such as an optical disk like a CD or DVD.
• the output of the photodiode can be directed towards different inputs of the operational amplifier 202 in the first and second phase.
• the circuit can compensate for both input offset voltage and bias current errors on any type of operational amplifier and enable a high degree of precision to be maintained over a wide range of operating conditions.
• the operation of the circuit can be divided into two phases. Phase one being input acquisition and phase 2 being output acquisition.
• the input acquisition and output acquisition loops 204 and 206 can include buffers 210 and 212 as well as sampling capacitors 214 and 216. Buffers 210 and 212 can be simple source followers with Class AB output stages for drive capability.
• the first phase can be an Input Signal Acquisition phase. In the first phase, switches Sl, S3, S6 can be closed such that current can pass through them. Switches S2, S4, S5 can be open such that current is blocked from passing through them.
• the input acquisition loop 204 is closed around the operational amplifier 202 and buffer 210. Summing the currents at the input to operation amplifier 202 we have:
• the second phase is an Output Signal Acquisition phase.
• Switches Sl, S3, S6 are open.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Amplifiers (AREA)

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• 2008
  • 2008-05-28 US US12/127,912 patent/US7760015B2/en active Active
• 2009
  • 2009-03-09 EP EP09720874A patent/EP2266202A4/de not_active Withdrawn
  • 2009-03-09 WO PCT/US2009/036544 patent/WO2009114474A2/en not_active Ceased
  • 2009-03-13 TW TW098108289A patent/TW200945767A/zh unknown

Non-Patent Citations (1)

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